I. Field of the Invention
The present invention relates generally to hybrid vehicles and, more particularly, to a system for selectively consuming and storing electrical energy in the hybrid vehicle.
II. Description of Material Art
Hybrid vehicles are enjoying increased popularity and acceptance due in large part to the cost of fuel for internal combustion engine vehicles. Such hybrid vehicles include both an internal combustion engine as well as an electric motor to propel the vehicle.
In the current design for both consuming as well as storing electrical energy, the rotary shaft from a combination electric motor/generator is coupled by a drive belt to the main shaft of an internal combustion engine. As such, the rotary shaft for the electric motor/generator unit rotates in unison with the internal combustion engine main shaft at the fixed pulley ratio of the hybrid vehicle design.
A control circuit controls and varies the torque of the electric motor/generator unit between a negative value and a positive value. When the control circuit sets the torque of the electric motor/generator unit to a negative value, the main shaft from the internal combustion engine rotatably drives the electric motor/generator unit in a generator mode thereby storing electrical energy in one or more batteries contained within the vehicle. Conversely, when the control circuit sets the torque to a positive torque, the electric motor/generator unit acts as an electric motor to increase the torque on the internal combustion engine main shaft thus consuming electricity from the battery and providing driving power for the hybrid vehicle.
These previously known hybrid vehicle designs, however, have encountered several disadvantages. One disadvantage is that, since the pulley ratio between the electric motor/generator rotary shaft and the internal combustion engine main shaft is fixed, e.g. 3 to 1, the electric motor/generator is rotatably driven at high speeds during a high speed revolution of the internal combustion engine. For example, in the situation where the pulley ratio between the electric motor/generator rotary shaft and the internal combustion engine main shaft is 3 to 1, if the internal combustion engine is driven at a high revolutions per minute of, e.g. 5,000 rpm, the electric motor/generator unit is driven at a rotation three times that amount, i.e. 15,000 rpm. Such high speed revolution of the electric motor/generator thus necessitates the use of expensive components, such as the bearings and brushes, to be employed to prevent damage to the electric motor/generator during such high speed operation.
A still further disadvantage of these previously known hybrid vehicles is that the electric motor/generator unit achieves its most efficient operation, both in the sense of generating electricity and also providing additional power to the main shaft of the internal combustion engine, only within a relatively narrow range of revolutions per minute of the motor/generator unit. However, since the previously known hybrid vehicles utilized a fixed pulley ratio between the motor/generator unit and the internal combustion engine main shaft, the motor/generator unit oftentimes operates outside its optimal speed range. As such, the overall hybrid vehicle operates at less than optimal efficiency.
A still further disadvantage of these previously known hybrid vehicles is that the electric motors were able to generate appreciable torque only at low engine speeds. As such, the electric motor was able to provide additional torque to the internal combustion engine only at low engine speeds, including engine start up. This, in turn, necessitated relatively larger internal combustion engines in order to obtain acceptable performance which resulted in a decrease in fuel efficiency for the hybrid vehicle.